Weather Warning Criteria

To help you decide which weather warnings are suitable for your purposes, please read the definitions below, and then consult the criteria chart at the bottom of the page.

Severe Weather Warning

MetService will issue a Severe Weather Warning whenever there is an expectation that any of the following weather conditions will occur within the next 24 hours:

• Widespread* rainfall greater than 50 mm within 6 hours or 100 mm within 24 hours;
• Widespread* snowfall below 1000 metres on the North Island or 500 metres on the South Island with a snow depth of 10 centimetres within 6 hours or 25 centimetres within 24 hours;
• Widespread* severe gales with a minimum mean speed of 90 km/hr or frequent gusts exceeding 110 km/hr.

*"Widespread" means over an area of 1000 square kilometres or more.

Severe Weather Watch

MetService will issue a Severe Weather Watch whenever there is an expectation that conditions may deteriorate to the thresholds specified for the issue of a Severe Weather Warning:

• After the next 24 hours but within 48-72 hours, or
• If there is a high level of uncertainty within the next 24 hours.

Special Weather Advisory

MetService will issue a Special Weather Advisory whenever a weather event is likely to cause significant disruption to the general public or specific industry groups within the next 48 hours, but the weather is not expected to deteriorate to an extent that would require the issue of a Severe Weather Warning.

MetService may also issue a Special Weather Advisory following a severe storm that caused widespread disruption and damage in order to assist with any post-storm operations.

Road Snowfall Warning

MetService will issue a Road Snowfall Warning for the Desert Road, the Porter's Pass Road, the Lindis Pass Road, the Rimutaka Hill Road, the Milford Road, Arthur's Pass or Lewis Pass whenever there is a likelihood of snow settling on one or more of those roads within the next 24 hours.

Snow Otago Warning

MetService will issue a Snowfall Warning for South Canterbury and Otago whenever snow is expected to accumulate to a depth of 20 cm or more within the next 24 hours at or below an altitude of 1500 metres and conditions are not severe enough to warrant the issue of a Severe Weather Warning.

Snow Otago Warnings are primarily for the high country farming communities of South Canterbury and Otago.

Severe Weather Criteria Chart

Definitions:

• One Day [High] - Within the next 24 hours, with a high level of certainty
• One Day [Low] - Within the next 24 hours, but with a low level of certainty
• One-Two/Three Days - Between 24 hours and 48-72 hours from now